1. Pressure Changes D. Crowley, 2008

2. Pressure Changes • To be able to explain what happens to a diving bell when pressure changes

3. Compression (squashing) • Which states can you compress (solid; liquid; gas)? • Only gas can be compressed, as it is the only state which has particles far apart, with space to be squashed into

4. Compression ¼ the space, and the particles will hit the wall 4x as often (pressure quadruples) ½ the space, and the particles will hit the wall 2x as often (pressure doubles) Gas particles randomly hit the side wall

5. Pressure • The greater the depth, the greater the pressure (the weight of the water above compresses the water below) Pressure = gravity x depth x density Low pressure High pressure

6. The Bends • As divers go deeper into the sea, the pressure on their body increases, squashing the lungs (which are full of gas) to a smaller volume • Some of this high pressure gas (mainly nitrogen) can dissolve into the blood • If the diver surfaces too quickly the gas within the blood expands, producing large bubbles, which can hinder the flow of blood and other bodily processes

7. Diving Bell • A diving bell is an airtight chamber, open at the bottom • It is lowered underwater to help transport divers deep underwater, or as a rescue device • The pressure of the water keeps the air trapped inside the bell so the divers can still breathe

8. Making A Diving Bell • Almost fill the bottle with water • Make a model diving bell by putting a ball of plasticine onto the end of the syringe • Drop the model into the bottle, with the plasticine end downwards • If the model sinks completely, take it out and remove some of the plasticine – change the amound of plasticine until the model just floats near the top of the water • Fill the bottle completely with water • Squeeze the bottle and look at what happens to the syringe diving bell – record what happens

9. Recording findings

10. Recording findings

11. How It Works • The bell is ballast so it stays upright • As a diving bell is lowered, increasing pressure from the water compresses the gas in the bell • Adding gas keeps the air space the same as the bell descends in the water, as well as refreshing the air - this would become saturated with a toxic level of carbon dioxide and depleted of oxygen by the respiration of the divers if left for too long

12. How It Works • As you push on the bottle the air pressure in the bell decreases (the water pressure doesn’t change – it can’t be squashed) • The lower pressure makes the bell less buoyant (and more dense) so it sinks • When you release the balloon the pressure increases again and it floats back up (now less dense)